ENVIRONMENTAL EDUCATION SERIES
ENVIRONMENTAL QUALITY
Agriculture & Natural Resources
EXTENSION ENVIRONMENTAL EDUCATION, AUBURN UNIVERSITY, AL 36849-5647
Calibrating Your Home Fertilizer Equipment
ANR-745, 1992. By Charles Ogburn, Extension Agricultural Engineer (Retired),  Agriculture, Auburn University
It is extremely important that you properly apply granular fertilizer. Misapplication can result in inadequate fertility, striping of the lawn, and waste of fertilizer that may be leached to groundwater or lost in runoff, therefore, polluting surface waters. Proper application can be accomplished by properly calibrating the equipment you use to apply the fertilizer.

   There are two types of commonly used lawn spreaders, drop type and rotary (spinner). Drop spreaders provide an even, more precise distribution of granules, while rotary spreaders cover a wider swath, but distribute granules less uniformly.

   Even though the manufacturers of spreaders provide recommendations for settings and swath widths, you need to calibrate the spreader for each product to be used as well as each operation. The settings indicated on the product label should be used only as the initial setting and should be verified prior to use.

Drop-Type Spreaders
   The following steps can be used to determine the application rate for drop spreaders.

  1. Measure the width of the opening along the bottom of the spreader hopper to determine the swath width.
  2. Lay out a 3 ft. by 50 ft. strip of polyethylene. The width of the material used may vary, but should be at least 1 foot wider than the spreader.
  3. Fill the hopper about half full and adjust the spreader setting to the appropriate one indicated by the manufacturer, product label, or one that you feel will deliver the amount specified on the product label.
  4. While walking at normal speed alongside the plastic strip, push the spreader along the full length of the strip. This should be repeated 3 to 5 times.
  5. Fold the plastic to form a "V" so the product will settle to the center, sweep it up, and empty it into a container that can be used to weigh the material. When weighing, be sure to account for the weight of the container.
  6. Next, determine the amount of product delivered per 1,000 ft2. This is a two step procedure: a. Calculate area covered by the amount of product collected and weighed.
Area Covered (ft.2)    =    swath width (in.)
12		   x    number passes x 50 ft.

          b. Adjust this to amount of product that would be delivered to 1000 ft.2 area.

Lbs/1000 ft.2    =    Lbs of product collected x 1,000
Area covered (ft.2)
   Example:
    Swath width = 26 inches
    Number of passes = 3
    Amount Collected = 11 oz. = 0.69 lb.
      a. Area Covered    =    26 in.
12		    x    3    x    50 ft.    =    325 ft.2
      b. Lbs./1000 ft.2    =    0.69 lbs. x 1,000 ft2
325 ft.2		    =    2.12 lbs.

Rotary Spreaders (Spinners)
   The following steps can be used to check the delivery rate of a rotary spreader.

  1. Mark off a 1,000 ft.2 (20 ft. x 50 ft.) on a paved surface, or preferably lay out a 20 ft. x 50 ft. drop cloth.
  2. Add the product to be measured to the hopper, using the approximate amount you intend to apply. Adjust the spreader setting to the recommended setting or the one you feel is close to the desired rate.
  3. Apply the material uniformly to the area you have marked off.
  4. Sweep up and weigh the granules that were applied.
  5. Repeat this procedure until you arrive at a setting that delivers the appropriate amount specified on the product label.
   Rotary spreaders should also be checked for distribution of the product. The manufacturer's recommended swath width should be verified, even on new spreaders. This can be done by laying out a series of shallow pans in a line perpendicular to the direction of travel. Each pan should be about 1 ft.2 in area. They should be placed about 1 foot apart in a line that is 1½ to 3 times the recommended swath width. Push the spreader past the line of pans three times, going in the same direction. Measure the amount of product in each pan by weight at the center. For example, if the center three or four pans have 2 ounces of product in them and the pans 6 feet to the right and left of the spreader centerline have 1 ounce of product, the effective swath is 12 feet. Adjust the swath width during actual application for the most uniform distribution pattern.

Application Techniques
   It is best to begin spreading a lawn by covering a swath around the perimeter. (This gives you room to turn around and realign the spreader, as well as providing uniform coverage of border areas.) When spreading the lawn, attain normal operating speed in the border strip with the spreader closed. Open it when you reach the edge of the border area. At the other end, close the spreader as you enter the border strip, still at operating speed. Avoid leaving the spreader open when making turns or when it is stationary. When coverage problems occur (usually with rotary spreaders), reduce the setting to one-half the rate and cut the swath in half. Continue to walk in parallel swaths. Avoid operating the spreader backwards because most spreaders will dispense a different rate and provide less uniform coverage when pulled rather than pushed. Maintain a uniform walking speed to maintain a uniform application rate.

   Surface broadcasting fertilizers over the entire area of the root system of a tree or shrub is an effective and efficient method of application. About 80 percent of all fibrous roots are found in the upper 12 inches of soil, and many are found in the upper 6 inches. Therefore, a surface broadcast can easily reach a majority of the root system. If the root zone area is planted with ground-covers, grass, or other plants sensitive to high nitrogen levels, it may be necessary to water in fertilizer to prevent burns. To prevent burn, fertilizer application for trees in lawn areas can be split into two applications that are two weeks apart.

For more information, call your county Extension office. Look in your telephone directory under your county's name to find the number.
Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability.

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